--- zzzz-none-000/linux-4.4.271/net/sched/sch_fq_codel.c	2021-06-03 06:22:09.000000000 +0000
+++ hawkeye-5590-750/linux-4.4.271/net/sched/sch_fq_codel.c	2023-04-19 10:22:30.000000000 +0000
@@ -57,6 +57,7 @@
 	u32		flows_cnt;	/* number of flows */
 	siphash_key_t	perturbation;	/* hash perturbation */
 	u32		quantum;	/* psched_mtu(qdisc_dev(sch)); */
+	u32		drop_batch_size;
 	struct codel_params cparams;
 	struct codel_stats cstats;
 	u32		drop_overlimit;
@@ -133,17 +134,20 @@
 	skb->next = NULL;
 }
 
-static unsigned int fq_codel_drop(struct Qdisc *sch)
+static unsigned int fq_codel_drop(struct Qdisc *sch, unsigned int max_packets)
 {
 	struct fq_codel_sched_data *q = qdisc_priv(sch);
 	struct sk_buff *skb;
 	unsigned int maxbacklog = 0, idx = 0, i, len;
 	struct fq_codel_flow *flow;
+	unsigned int threshold;
 
-	/* Queue is full! Find the fat flow and drop packet from it.
+	/* Queue is full! Find the fat flow and drop packet(s) from it.
 	 * This might sound expensive, but with 1024 flows, we scan
 	 * 4KB of memory, and we dont need to handle a complex tree
 	 * in fast path (packet queue/enqueue) with many cache misses.
+	 * In stress mode, we'll try to drop 64 packets from the flow,
+	 * amortizing this linear lookup to one cache line per drop.
 	 */
 	for (i = 0; i < q->flows_cnt; i++) {
 		if (q->backlogs[i] > maxbacklog) {
@@ -151,15 +155,24 @@
 			idx = i;
 		}
 	}
+
+	/* Our goal is to drop half of this fat flow backlog */
+	threshold = maxbacklog >> 1;
+
 	flow = &q->flows[idx];
-	skb = dequeue_head(flow);
-	len = qdisc_pkt_len(skb);
+	len = 0;
+	i = 0;
+	do {
+		skb = dequeue_head(flow);
+		len += qdisc_pkt_len(skb);
+		kfree_skb(skb);
+	} while (++i < max_packets && len < threshold);
+
+	flow->dropped += i;
 	q->backlogs[idx] -= len;
-	sch->q.qlen--;
-	qdisc_qstats_drop(sch);
-	qdisc_qstats_backlog_dec(sch, skb);
-	kfree_skb(skb);
-	flow->dropped++;
+	sch->qstats.drops += i;
+	sch->qstats.backlog -= len;
+	sch->q.qlen -= i;
 	return idx;
 }
 
@@ -168,14 +181,14 @@
 	unsigned int prev_backlog;
 
 	prev_backlog = sch->qstats.backlog;
-	fq_codel_drop(sch);
+	fq_codel_drop(sch, 1U);
 	return prev_backlog - sch->qstats.backlog;
 }
 
 static int fq_codel_enqueue(struct sk_buff *skb, struct Qdisc *sch)
 {
 	struct fq_codel_sched_data *q = qdisc_priv(sch);
-	unsigned int idx, prev_backlog;
+	unsigned int idx, prev_backlog, prev_qlen;
 	struct fq_codel_flow *flow;
 	int uninitialized_var(ret);
 
@@ -198,22 +211,27 @@
 		list_add_tail(&flow->flowchain, &q->new_flows);
 		q->new_flow_count++;
 		flow->deficit = q->quantum;
-		flow->dropped = 0;
 	}
 	if (++sch->q.qlen <= sch->limit)
 		return NET_XMIT_SUCCESS;
 
 	prev_backlog = sch->qstats.backlog;
-	q->drop_overlimit++;
-	/* Return Congestion Notification only if we dropped a packet
-	 * from this flow.
+	prev_qlen = sch->q.qlen;
+
+	/* fq_codel_drop() is quite expensive, as it performs a linear search
+	 * in q->backlogs[] to find a fat flow.
+	 * So instead of dropping a single packet, drop half of its backlog
+	 * with a 64 packets limit to not add a too big cpu spike here.
 	 */
-	if (fq_codel_drop(sch) == idx)
-		return NET_XMIT_CN;
+	ret = fq_codel_drop(sch, q->drop_batch_size);
+
+	q->drop_overlimit += prev_qlen - sch->q.qlen;
 
-	/* As we dropped a packet, better let upper stack know this */
-	qdisc_tree_reduce_backlog(sch, 1, prev_backlog - sch->qstats.backlog);
-	return NET_XMIT_SUCCESS;
+	/* As we dropped packet(s), better let upper stack know this */
+	qdisc_tree_reduce_backlog(sch, prev_qlen - sch->q.qlen,
+				  prev_backlog - sch->qstats.backlog);
+
+	return ret == idx ? NET_XMIT_CN : NET_XMIT_SUCCESS;
 }
 
 /* This is the specific function called from codel_dequeue()
@@ -323,6 +341,7 @@
 	[TCA_FQ_CODEL_FLOWS]	= { .type = NLA_U32 },
 	[TCA_FQ_CODEL_QUANTUM]	= { .type = NLA_U32 },
 	[TCA_FQ_CODEL_CE_THRESHOLD] = { .type = NLA_U32 },
+	[TCA_FQ_CODEL_DROP_BATCH_SIZE] = { .type = NLA_U32 },
 };
 
 static int fq_codel_change(struct Qdisc *sch, struct nlattr *opt)
@@ -374,6 +393,9 @@
 	if (tb[TCA_FQ_CODEL_QUANTUM])
 		q->quantum = max(256U, nla_get_u32(tb[TCA_FQ_CODEL_QUANTUM]));
 
+	if (tb[TCA_FQ_CODEL_DROP_BATCH_SIZE])
+		q->drop_batch_size = min(1U, nla_get_u32(tb[TCA_FQ_CODEL_DROP_BATCH_SIZE]));
+
 	while (sch->q.qlen > sch->limit) {
 		struct sk_buff *skb = fq_codel_dequeue(sch);
 
@@ -417,8 +439,9 @@
 	struct fq_codel_sched_data *q = qdisc_priv(sch);
 	int i;
 
-	sch->limit = 10*1024;
+	sch->limit = 1024;
 	q->flows_cnt = 1024;
+	q->drop_batch_size = 64;
 	q->quantum = psched_mtu(qdisc_dev(sch));
 	get_random_bytes(&q->perturbation, sizeof(q->perturbation));
 	INIT_LIST_HEAD(&q->new_flows);
@@ -476,6 +499,8 @@
 			q->cparams.ecn) ||
 	    nla_put_u32(skb, TCA_FQ_CODEL_QUANTUM,
 			q->quantum) ||
+	    nla_put_u32(skb, TCA_FQ_CODEL_DROP_BATCH_SIZE,
+			q->drop_batch_size) ||
 	    nla_put_u32(skb, TCA_FQ_CODEL_FLOWS,
 			q->flows_cnt))
 		goto nla_put_failure;
@@ -629,7 +654,7 @@
 	.walk		=	fq_codel_walk,
 };
 
-static struct Qdisc_ops fq_codel_qdisc_ops __read_mostly = {
+struct Qdisc_ops fq_codel_qdisc_ops __read_mostly = {
 	.cl_ops		=	&fq_codel_class_ops,
 	.id		=	"fq_codel",
 	.priv_size	=	sizeof(struct fq_codel_sched_data),
@@ -645,6 +670,7 @@
 	.dump_stats =	fq_codel_dump_stats,
 	.owner		=	THIS_MODULE,
 };
+EXPORT_SYMBOL(fq_codel_qdisc_ops);
 
 static int __init fq_codel_module_init(void)
 {